Code hacks to change menu theme .. suppose we are customizing the design for "front" custom menu

1. Update outer structure by hook

function mytheme_menu_tree__menu_front(&$variables) {
     
    return '<ul class="links inline clearfix">' . $variables['tree'] . '</ul>';
}

2. To Add new css to li

The mobile sliding menu module integrates the mmenu jQuery plugin for creating slick, app look-alike sliding menus for your mobile website.